Electrical resistance apparatus



A. M. LEVY ELECTRICAL RESIST ANCE APPARATUS Feb. 7, 1928.

ori inal Filed Sept. 21. 19 0 ll f 9 w m a M m T1 4 J9 A Patented F elm .7, 1928.

U-NrrEn'sT rEs PATENT OFFICE.

mon mom LEVY, OF NEW YORK, N. Y... ASSIGNOR OF ONE-FOURTH TO JULIUS HOCHMAN AND ONEFOURTH TO MAURICE SAMBURG.

- ELECTRICAL RESISTANCE APPARATUS.

Application-filed Septemper 21, 1820, Serial No. 411,778. Renewed February 20, 1925.

My present invention relates to electrical resistance apparatus and more particularly to apparatus of the compression type.

' It'is an object ofthe invention to provide apparatus of the above type simple and relatively inexpensive in construction, the ohmage of which while readil adjustable within fine limits, shall, nevert eless, not be subject touhdsired fluctuation or. variation, even when left in circuit continuously for ,a sub-' stantial period of time.

Certain preferred features of the invention -reside in the construction of a resistance unit embodying a container preferably cylindrical in shape, substantially filled'with comminuted resistance material, the walls of the container being preferably of thin heat-resisting ma'terial, the container being completely closed to prevent escape of even the smallest particles of the resistance material, part of said container being readily displaceable to vary the compression and, there- 'fore the resistance of the included medium, the interior ofthe container wall contacted 'by the resistance inedium being preferably devoid of projectionsof protuberances.

Although the best results as regards con- 'stancy-v of resistance or conductivity of the unit for any particular setting are obtained when all of the preferred features are employed, it will be understood that satisfac tory operation may bebrought about for certain purposes when one or more of these features are not utilized.

Referring now to the drawings,

Fig. 1 is a "iew in longitudinal section showing a preferred application of my mvention; i

Fig. 2 is a fragmentary transverse sectional view taken along the line 2-2 of Fig. l, and;

Fig; 3 shows a fragment of a modified form of diaphragm.

Referring now to the drawings, I have shown by way of example a rheostat comprising a common form of enclosing casing 1 having a cover '2. and an operating handle 3 with a pointer 4 to indicate the setting of the rheostat upon the usual form of scale (not shown) on the cover.

Within the casing 1, I provide a resistance unit comprising a container 5 of a substanforms of curved surface may be employed.

Enclosed within the container 5 to c0mpletely fill the same is a compression resistance medium 8. This medium comprises preferably a mixture of comminuted graphite and mica subdivided into smallflakes, although any appropriate resilient mineral fiber may be used in this mixture in place of the mica. Other types of permanently re: sili ent compressible resistance medium such as shredded carbonized cloth may also be used. My invention does not reside in the particular resistance medium per se. Any substance or mixture of substances preferably in comminuted form, the conductivity of which will increase with the pressure applied thereto is satisfactory, provided it is either inherently resilient, or is associated with resilient means to effect increase of resistance when pressure is released. a

The container 5 has a flange or rim 9 formed integal therewith at it upper edge, the said flange furnishing a rest for the container within the casing 1. By preference an insulating heatresisting gasket 10 is interposed bctween support bracketsll secured to the inside of the casing, upon which brackets the gasket rests, the container in turn resting upon said'gasket. The container extends downwardly from the suppprt brackets and the entire surface thereof is freely exposed within the casing 1, for a purpose which will appear below.

Preferably a diaphragm 12, completel closes or seals the container against egress of even the smallest particle of the cpmminut-ed resistance material contained therein. The diaphragm by preference is formed of ashestos or equivalent mineral fiber compressed into a thin felt and held referably between layers of asbestos cloth, a though wire mesh may be employed for this purpose. If desired, a suitable metal diaphragm 50 (see Fig. 3) may be used instcad'of the asbestos diaphragm, this diaphragm having preferably pressed out circumferential grooves. 6 The diaphragm iselectrically insulated from the container preferably by a second insnlat 'ing gasket. 12; of heat-resisting material interposed between the flange t) of the containcr'and the rim 14 of the diaphragm. \Vhen t the asbestos diaphragm is used, the gasket 12) maybeomit'ted.

The diaphragm is firmly secured at its rim with respect to the container, by means of bolts 15 which extend transversely through 13 the rim 14 of the diaphragm, the gasket 13, the flange!) of the container, the gasket 10 and the brackets 11.-' The openings 16 and 17 in the metallic diaphragm and in the container flange through which the bolts extend 0 are preferably substantially larger than the diameter of the bolts and s aced therefrom to prevent a short-circuiting etween the diaphragnrand the container.

The container 5 constitutes one of the electrical terminals of the resistance unit, an electrical conductor 18 being connected thereto preferably at the bottom thereof and extending to the exterior through an outlet 41 in casing-1. The other electrical terminal preferably comprises a post 19.to which is connected a conductor 18, extending through an outlet 41' in the casing 1. The post 19 extends upwardl or outwardl from the diaphragm and is preferably c amped ceritrally thereto by means of a pair .of clamping washers 20 and 21 at opposite sides thereof, a nut 22 threaded u on the lower end of the st serving to c amp the diahragm l2 etween thewashers 20 and 21. y preference the lower washer 21 is extended outwardly beyond the upper washer :1 'and beveled as at 23 so that the surface thereof in contact with the resistance medium shall be substantially continuous with the adjoining surface of the diaphragm as shown. The nut is preferably countersunk within the lower washer as shown zit-24, the parts being so arranged that the nut and the threaded end of the post terminate-sub- 60 stantially flush with the washer in order to provide asubstzmtially smooth and continuous surface without sharp projections or extensions in contact with the resistance medium. 7

Means is provided for adjusting the press'uroupon the resistance medium 8 in the' container to effect any electrical resistance within the range of the apparatus. This means'may'comprisca cylindrical cam wall 27 rising from the upper end of the container and having a pair of cams in the form of helical grooves 28 in which fit pins :39 secured to and extending outwardly from a flange 30. upon a plate 31 concentric with t and of slightly smaller diameter than the cam wall. The plate 31 rests upon a washer 32 which in turn rests upon a shoulder 33 on post 19, a nut 34 securing the plate against upward movement with respect to 7 post 19. The plate 33 is free to revolve n around post .19 as an axis, and governsthe Vertical displacement of said post. A coil spring 35 preferably encircles the post and pre: scs at. its upper end against the plate 31' and rests at its lower end upon a retainer 7n plate 36.

Preferably the periphery 37 of retainer plate 36 together with the periphery l i of the closure diaphragm'12 are clamped be-' tween the cam wall 27 and the flange 9 of the eylindrical side wall 6 bymeans ofthe bolts 15 which extend through cam wall 27, retainer plate 36, diaphargm 12, gasket 121-, 7 container flange 9, gasket 10 and bracket 11. The handle 3 upon the cover of the rlnostat casing is connected-with the container 5 in such manner that rotation thereof will cause corresponding increase or decrease of. the compression of the resisting medium. For this purpose the handle .has secured thereto by any desired means an arm 38 provide'd at its extreme end with a fork 39 straddling a pin'40 upon the plate 31.

It will be understood that as the handle 3 is turned the arm 38 will turn therewith 05 and through the fork 39 and pin 40 it will cause a rotation of the disk 31. For a cloekwise rotation of the handle 3 in the specific embodiment shown, the pins 29 will trarel. downwardly along the cam grooves 28 and the (plate 31 wilt thereby be forced downwar ly and with it the post 19. This causes a depression of the diaphragmatic cover 12 against the opposition of spring.35 and a corresponding compression of the resisting, medium against the-end or'bottom wall 7, with the consequent decrease in resistance, until the diaphragm reaches the limiting depressed position shown in dotted lines. WV hen the handle 3 is turned in the opposite or counter-clockwise direction the plate 31 is caused to rise by reason ofthe upward component of the travel of pins 29 within the cam grooves .28 and the diaphragmatic cover 12 rises therewith, the expansion of the compressed resisting medium andthe expansion of spring 35 also tending to press the diaphragm upwardly. The compression upon the resisting medium is thus decreased and the electrical resistance increased. The limiting position corresponding to maximum ohmage appears in full lines on the draw ings; By'preference the apparatus is so arranged as to cause the resistance medium to be completely short-circuited for one ex tremeposition of the handle. For thispurpose the conductors 18 and 18' have contacts 42 and 42 respectively intermediate their ends and within the casing 1,said contacts -tron in the resistance unit.

r I have discovered that'by the use ofa resistance unit of the character set forth, I achieve the desirable result of substantial constancy of conductivity for any particular setting, regardless how lon the circuit in which the resistance unit is employed re? mains closed. My resistanee'unit is, therefore, of particular utilit in electrical regulators and-controllers w iere it is important to maintain a substantial constancy of resistance and in relatively inexpensive unit i can, therefore,

used as a substitute for the considerably more expensive electrical resistance coil or grid resistances commonly used for such purposes. V

In operation,'the thin-walled container 5 quickly becomes heated as the current generates heat by its sistance medium. e ventilating current of air through passages 25 and 26 in the easing coming mto contact with the entire surface of the container exposed thereto, effectively carries 'ofi the heat generated after the current has been on for a short period of time. Apparently, the tem ratureof the container walls remains su tantially con-- stant after the circuit has been closed a very short interval of timeand, therefore, no ex- ;pansion or contraction thereof takes place thereafter.- It seems to follow that. the pressure exerted by the walls u n the resistance medium does not vary an ,'.therefore, that no chan es in ohmage will occur. I have cstablishe experimentally that the ohmage of my unit remains substantially constant for any setting regardless .how long the circuit Lanains closed. It-is to be understood that the foregoing theory-as to the reason for this uniformity is merely tentative and may be subject to modification.

Subs antial constancy of ohmage for any particular setting is reliably maintained in the of a unit as set forth embodying a container having thin walls of heat-resisting material, preferably entirely exposed to the air, the vessel being completely sealed against escape'"of the resistance medirun contained therein, there being a total absence of protuberances or projections extending into the resistance medium. installations it is also desirable, though not essential, that the walls of the container be not plane but convex or concave exteriorly, preferably the former, although in" the case position ind cating zero re-.

a 'age through the re'--.

In the case of smaller .of larger installations such construction is found to be of greater importance when the best results are to be obtained. It seems that ordinary plane walls, more. particularly in larger installations, have a tendency to sag inwardly under heat and to thereby change the ressure upon the resisting medium. This pro ably accounts for varying conductivities. With convex or concave walls of the character set forth, on the other hand, the conductivitymaintains a constant value for any" particular setting. "lhis is probably ex: plained atleast in part,,by the fact'that such convex or concave walls have no tendency to sag.

'It will, of course, be understood that my unit may be used in resistance starting boxes or in other apparatus which are not kept in circuit for more than a few seconds at a time and in which anysubstantial rise in conduc tivity is not particularly undesirable. In'

that event although I prefer to use the form of container shown and described, and although superior results are obtained by its use, sufiiciently good results can be obtained where the walls of my form of container are thick rather than thin, plane rather than curved and where the container is not completely sealed.-

My resistance unit includes a completely closed container, the'closure of which in the preferred embodiment is a diaphragm to permit displacement and compression of the resistance medium and .to prevent escape thereof. It will be understood, however, that/the broader features of my invention can be carried out by the use ofa closed container in which-any part of the wall thereof is flexible even though such wall portion be not resilient and in which-compression is of fected by displacing a. portion of the containcrwall, utilizing the capacity of yield of the flexible portion, even though the pressure be not applied directly at such flexible portion.

It is-also to be noted that although I prefer to employ a metallic container, part or all of the wall may be of heat-resisting insulatin material. i

It will be understood that as the resistance medium is compressed to reduce the ohmage, the pressure is directly exerted against the bottom'T, the side wall of the container is placed under tension and the gaskets 10 and 13 under compression; In some resistance devices, particularly when delicate and low ohmage control is wanted, it is desirable to place the resistance medium under considerable compression. The me: tallic container although thin-walled will, in such cases, withstand the substantial tensile force applied thereto, and the gaskets -will be of increased efiectivcness under large {part of -said resistance material, said clo- -sure heing displaceable to vary the compres-.

sion and the electrical resistance of said enclosed material, meansfor displacing said closure and electrical terminals for said conand thereby tainer. Y 1 l 2. An electrical resistance apparatus comprising in' eombinatioma sealed;heat-resisting container having relatively thin end walls, comminiited resistance material substantially filling said container, one of said walls of said container-{being of flexible metal, means for exerting pressure upon the resistance material whereby the electricalresistanee imposed by the apparatus may be varied in accordance with the degree of pressure exerted upon the flexible wall. 7

3. The combination set-forth in claim 2 in which one of the end walls of the container is of thin metal and constitutes a ter-.

minal.

4. An electrical resistance PPt1ratuscom-- tainer, said container having a closure to prevent escape of any pa rt of said resistance material, said closure being displaceable to vary the compressionand the electrical resistance of the enclosed material, the terminals of said 'unit being: one at said end wall and the other at said closure, saidapparatus including operating means for displacing said closure, and thereby varying atwill the resistance imposed by said apparatus.

5'. An electrical resistance apparatus comprising ina-onlbiuation, a container having end walls. one of which is of rclatively'thiu metal. a. heat-resisting wall element connecting said end walls to form a sealed container, and eonnuiuutcd resistance material filling said container: said parts being constructed and arranged to permit displacement of one of-said end walls; relative to the otherto vary the compression and electrical res st.-

ance of said resistance material, said apparatus including ,operating means for dis-v placing said closure, and thereby varying at will the resistz'ince imposed by said .ppa-' ratus.

.a-sphere with its convexity on-tlieei rterior' medium.

6. An electrical resistance unit, comprising in combination, a container'having a curved side wall, a curved end wall continuous therewith, said end wall being of a'thin heatresisting material, comminuted resistance material enclosed-within said container, said container havinga'elosure to prevent escapeof any part of said resistance material, said closure being displaceable to vary the compression and the electrical resistance-ofs the enclosed material. 7 Y 7. An electrical resistance apparatus co'm prising in combination; 'a-container formed of an integral piece of thin metal "and com-,- prising a cylindrical side wall and an end wall concave internally and convex exter-"f nally, a resistance medium filling said container, a closure for said container, and'op crating means for 'displacinguiaid closure, varyingat the resistance imposed by said apparatus. 8. An electrical resistance apparatus comprising. in combination, a container having a cylindrical side wall,"and amend wall of thin sheet'metal in the form of a segmeht-of said end wall constitutingan electrical ter-"*' minal, resistance medium filling said container, a closure for 'said container,- and 6perating'means for :displacing said closure, and thereby varying-at will the resistance imposed b said apparatus;

- 9. An e ectricalresistance unit comprising in combination, an integral cylindrical heath resisting container having a mineralfiber diaphragm closure, a compressible resistance medium enclosed in saidcontainer, and

means operable from the exterior of the con tainer for causing deflection of saidclosure. to vary the compression of said resistance 10. An electrical resistance unit compris--'- ing in combination, a-cylindrical heat-resist-' in g container ofthin material having a metallic end wall, an asbestos. diaphragm closure,

a compressible resistance medium 'substantially filling said container, and means op-- erating upon said closure for deflecting the same to yary the compression of said resistance medium.

]l. The combination set forth in claim 6, in which the container is formed ol an illtegral piece of thin metal, and com nises a cylindrical side wall and an end wall con care internally and convex exterually, and in which the closure is a flexible diaphragm sealing said container.

12. An electrical resistance apparatus comprising in combination, a container havinga cylindrical side wall, a metallc end wall and a fle nble diaphragm closure, an elec-- trrcal term nal secured to said closure, and

cant means cooperatin; with said closure to cause depressionof e'-;.d.c. di aphragm in responseto a rotary actuating movement.

and projecting outwardly therefrom, a cam- .wall rising from said container, cam pins rigid with j'said terminal and cooperating .Wlth said cam wall, and means for causing movement of said pins at will along said cam l depressing--said diaphragmatic closure.

- -14.. An electrical resistance unit "compris- 'in in; combination, aheat-resisting thinwa led container a diaphragmatic flexible closure therefor, an electrical terniinal secured centrally to said closure and extending upwardly therefrom, a cam wall secured to said container and extending I upwardlytherefrom and havinga pair of cam grooves,

a flanged plate rotatable about said, terminal and having pins extending outwardly from theflangethereof into said cam grooves, a spring coiled about said terminal and pressing at one end against said flanged disk, and a retainer for the other end of said spring, said retainer being rigid withsaid container. 15. An electrical resistance apparatus comprising a sealed container having a metallic bottom wall and a yielding top wall, a relatively unyielding, heat-resisting side wall constituting an electrical terminahcompression' resistance medium substantially filling said container,.casing enclo ing said container electrically insulate and spaced therefrom and means accessible from the exterior of said casing fofexertingvariable pressure against said yielding'top wall.

- 16. An electricalresistance apparatus com-' prising a sealed container having a relative-' l v unyielding, heat-resisting side wall, and

end walls, one of'said walls being yielding,

end wall terminals, a resistance 'lmedinm in said container, said container ing con structed to permit approach ofsaid yielding end wall toward the other, a casing enclosing' said container insulated and spaced therefrom, said casing having ventilating passages, and means accessible from the exterior of said casing for causing relative displacement of said end walls to vary the compression and electrical resistance of said resist ance medium. a

17. An electrical resistance apparatus comprising in combination, a container having a thin, heat-resisting side walk, a metallic end wall convex in form and a diaphragmatic closure wall, a compression resistance medium within said container, an enclosing casing, mean! supporting said container within said. casing and insulated therefrom, an operating handle upon the exterior of said casing, and means connecting said handle to said resistance medium to cause compression thereof responsive to 425 actuation of said handle.

18. An electrical resistance apparatus comp r1s 1ng in combination, a contalner having a cylindrical side wall, a convex end wall continuous therewith, resistance medium within said contalner, longitudinally movable means for varying the compression of said resistance medium, cam means for causing movement of said'means responsive to a rotary movement, an enclosing casing-for said container insulated therefrom, operat' ing means accessible from the exterior of said casing, and a connecting element between said operating means and said cam means.

. 19. An electrical resistance unitcomprising in combination, a closed container, comminuted resistance material substantially filling the same, and an electrical terminal "extending from the exterior through a wall of said container into contact with said resistance material, the portion of said terniinal within said container being substantially continuous with the container wall to avoid sharp metallic edges, corners or projections within the contalner.

20. An electrical resistance apparatus comprising in combination, a resistance unit including a heat-conducting container having a side wall and an end wall, said container being filled with compressionresistance ma' terial, a displaceable closure for said container, a support, a portion of said container adjacent said closure resting upon said sup-- and having a supporting part at its open end,

, compression resistance material fil ng said container, a diaphragm closing the n end of said container, a casing having a upport therein upon which said supporting parts rest, the body of said container extending downwardly from said support and spaced at aH- parts from the walls and bottom of said casing, said casing having ventilating apertures, whereby excess heat generated in said unit will be effectively eliminated.

. 22. An electrical resistance apparatus com- =prising in combination, a compression resistance unit having terminals, an enclosing casing within which said unit is mounted, electrical conductors leading from said terminals through said casing, an operating handle upon the exterior of said casing for varying the pressure upon said resistance unit, and a die for establishing an electrical contact between exposed portions of said conductors to tact with said material to permit expansion thereof under heat, and ineans for subjectin v the resistance material to'compression in or er to adjust the resistancethereof, at least one of the yielding metal parts .in eontact with. the resistance materialbeing substantially smooth and free from projections;

24. In a compression rheost-at, a container having a stationary endanda displaceable resistancev material housed therein, yielding metal parts in 0011- closure plate, finely divided resistance mate- 15 rial in said container,-a rigid retaining wall confining said material between said end and said closure, means to displace the closure for compressing the material inorder to create paths of conductivity therethrough, said container being constructed to allow for the expansion of said niaterial'fwhen the same'becomes heated and to radiate the heat created therein.

Signed at New York city," in the county of 25 New York, and State of New York, this 20th day of September A. D. 1920.

AARON MICAHLEVY. 

